The invention pertains to methods and apparatus for measurement of joint laxity and stiffness.
The evaluation of joint function is important in the assessment, diagnosis, and treatment of injuries and diseases that affect joint function. Typical methods of evaluation rely on a displacement of a limb by a clinician or physician who applies a force to produce the displacement. The usefulness of such methods of evaluation is limited because of the subjective nature of both the force and the displacement measurements, and meaningful comparisons of measurements by different clinicians/physicians or of measurements before and after therapy are not possible. As a result, such measurements are generally not well-suited for the evaluation of the effectiveness of any particular therapy or surgery, nor can such measurements serve as reliable indicators of the extent of joint degeneration or injury.
Other methods of assessing joint function involve static imaging of the joint with X-rays or other imaging techniques. Unfortunately, static imaging does not permit accurate assessment of actual joint function. Accordingly, improved methods and apparatus of assessing joint function are needed.
According to a first aspect of the invention, instrumented arthrometer systems are provided that numerically measure, record, and graphically display laxity of a body joint, for example, the shoulder (glenohumeral) joint. The arthrometer systems can measure, record, and display stiffness as well. Such instrumented arthrometer systems provide simple, inexpensive joint assessment. As used herein, joint laxity refers to a functional relationship between torque or force applied to a joint and the resulting translational or rotational displacement. Measurement or assessment of joint laxity includes measurement of displacement, force, or both force and displacement. To measure joint laxity, a clinician applies a force or torque to a bone, group of bones, or a joint-reference location of a subject, and the force or torque is measured with a load cell, force glove, or torque glove, and transmitted to a data logger such as a general-purpose personal computer, a handheld computer, or a dedicated computer. Joint displacement is measured using one or more translational and/or one or more rotational detectors. Displacement data also is delivered to the data logger and recorded. The recorded force/displacement or torque/displacement data is processed and displayed with a software program that can be stored on a computer-readable medium such as a floppy disk. A liquid crystal panel, a cathode ray tube monitor, or a printer can be provided to display the recorded data.
For simultaneous measurement of translations in three dimensions, three translational detectors can be provided, or one or more translational detectors that detect translations in multiple directions. Multiple rotational detectors can be used to obtain yaw, pitch, and roll simultaneously.
Data recording and display are conveniently performed using a general purpose personal computer and an associated program. Data can be stored in a form suitable for importation into a spreadsheet program or other data analysis or display program. For portable instrumentation, a laptop computer or a handheld computer can be used. A dedicated processor or computer system, or embedded processor also can be used, if desired.
Translations and rotations can be measured with, for example, the spatial tracking systems available from Polhemus Corporation, Colchester, Vt. These systems use electromagnetic position and orientation measurement devices that permit measurements of joint/bone translations and rotations without cable connections to the subject.
In an embodiment, a clinician applies a force/torque to the joint under measurement using a force/torque glove. The clinician wears the force/torque glove and applies the force/torque manually. The applied force/torque is recorded by the data recording system. In such systems, clinical measurements do not require an additional force/torque applicator. The clinician manipulates the subject""s joint or limbs directly, but an instrumented force/torque applicator alternatively can be used.
The instrumented arthrometer permits the acquisition of accurate, objective joint laxity data (i.e., quantitative force-displacement data). Such joint laxity measurements are useful especially for assessing subjects who have suffered capsulo-ligamentous disruption, who have undergone ligamentous surgery, or who are under observation for other conditions. The injured joint can be measured readily for comparison with a similar measurement of the contralateral (healthy) limb to identify differences in ligamentous laxity in various translational planes or about various axes of rotation. In this way, the instrumented arthrometer assists the clinician with diagnosis, aiding in assessing the success or failure of reconstructive surgery, while also providing data for developing a rehabilitation program. In addition, the instrumented arthrometer is largely free of operator error, and can provide reliable and prompt input to medical providers, insurance companies, and health-maintenance organizations for assessing the appropriateness and effectiveness of recommended courses of treatment.